Using a case when to know if date format is right - oracle

Question

I want to migrate a table which contains some columns with dates. The issue is my dates are often in dd/mm/yyyyy HH24:MM:YYYY format. But sometimes it appears that the format is only dd/mm/yyyy, or blank.
I guess that's why I'm getting ORA-01830 when I'm trying to migrate the datas.
I tried
CASE
WHEN TO_DATE(MYDATE,'DD/MM/YYYY')
then TO_DATE(MYDATE,'DD/MM/YYYY 00:00:00')
END AS MYDATE
But I'm not sure if it is possible to test the date format (and ofcourse it's not working).
Thank you

Answer 1

TO_DATE cannot test date format, but you can do it. If Lalit's answer would not be enough, try something like
select
case when my_date like '__/__/__' then to_date(my_date, 'dd/mm/yy')
when my_date like '__-__-__' then to_date(my_date, 'dd-mm-yy')
...
end

Answer 2

So you have the data type issue. DATE is stored as string literal. As you have mentioned that the date model has the DD/MM/YYYY part same, just that the time portion is either missing for some rows or the entire value is NULL.
For example, let's say your table have the values like -
SQL> WITH dates AS(
2 SELECT 1 num, '29/12/2014 16:38:57' dt FROM dual UNION ALL
3 SELECT 2, '29/12/2014' FROM dual UNION ALL
4 SELECT 3, NULL FROM dual
5 )
6 SELECT num, dt
7 FROM dates
8 /
NUM DT
---------- -------------------
1 29/12/2014 16:38:57
2 29/12/2014
3
SQL>
TO_DATE with proper format model should do the trick.
Let's stick to a format model first.
SQL> alter session set nls_date_format='dd/mm/yyyy hh24:mi:ss';
Session altered.
Now, let's use TO_DATE to explicitly convert the string literal to date.
SQL> WITH dates AS(
2 SELECT 1 num, '29/12/2014 16:38:57' dt FROM dual UNION ALL
3 SELECT 2, '29/12/2014' FROM dual UNION ALL
4 SELECT 3, NULL FROM dual
5 )
6 SELECT num, to_date(dt, 'dd/mm/yyyy hh24:mi:ss') dt
7 FROM dates
8 /
NUM DT
---------- -------------------
1 29/12/2014 16:38:57
2 29/12/2014 00:00:00
3
SQL>